Cleanup: provide our own qOverload<> implementation.

This is only in Qt 5.7 and therefore can't be used in Qt 5.5 and 5.6
builds. Moreover, we can't simply reuse Qt's version owing to
licensing concerns.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

2 files changed, 23 insertions, 13 deletions

diff --git a/core/qthelper.h b/core/qthelper.h
index 2cc7dfec4..cbe2b77f0 100644
--- a/core/qthelper.h
+++ b/core/qthelper.h
@@ -116,6 +116,21 @@ void moveInVector(Vector &v, int rangeBegin, int rangeEnd, int destination)
 		std::rotate(it + destination, it + rangeBegin, it + rangeEnd);
 }
 
+// Qt overloads some signals(!) which can't therefore be used in connect() calls with
+// pointers-to-member functions where the signatures of signal and slot don't match perfectly.
+// For this case, Qt 5.7 provides the qOverload<> helper.
+// Since we still support Qt 5.5 let's reimplement it here.
+#if QT_VERSION < 0x050700
+template <typename... Args>
+struct QOverload {
+	template <typename Ret, typename Class>
+	static Ret (Class::*of(Ret (Class::*fun)(Args...)))(Args...)
+	{
+		return fun;
+	}
+};
+#endif
+
 #endif
 
 // 3) Functions visible to C and C++
diff --git a/desktop-widgets/filterwidget2.cpp b/desktop-widgets/filterwidget2.cpp
index 17e43f941..f106c354e 100644
--- a/desktop-widgets/filterwidget2.cpp
+++ b/desktop-widgets/filterwidget2.cpp
@@ -52,21 +52,16 @@ FilterWidget2::FilterWidget2(QWidget* parent) :
 	connect(ui.minVisibility, &StarWidget::valueChanged,
 		this, &FilterWidget2::updateFilter);
 
-	// We need these insane casts because Qt decided to function-overload some of their signals(!).
-	// QDoubleSpinBox::valueChanged() sends double and QString using the same signal name.
-	// QComboBox::currentIndexChanged() sends int and QString using the same signal name.
-	// Qt 5.7 provides a "convenient" helper that hides this, but only if compiling in C++14
-	// or higher. One can then write: "QOverload<double>(&QDoubleSpinBox::valueChanged)", etc.
-	connect(ui.maxAirTemp, static_cast<void (QDoubleSpinBox::*)(double)>(&QDoubleSpinBox::valueChanged),
+	connect(ui.maxAirTemp, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
 		this, &FilterWidget2::updateFilter);
 
-	connect(ui.minAirTemp, static_cast<void (QDoubleSpinBox::*)(double)>(&QDoubleSpinBox::valueChanged),
+	connect(ui.minAirTemp, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
 		this, &FilterWidget2::updateFilter);
 
-	connect(ui.maxWaterTemp, static_cast<void (QDoubleSpinBox::*)(double)>(&QDoubleSpinBox::valueChanged),
+	connect(ui.maxWaterTemp, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
 		this, &FilterWidget2::updateFilter);
 
-	connect(ui.minWaterTemp, static_cast<void (QDoubleSpinBox::*)(double)>(&QDoubleSpinBox::valueChanged),
+	connect(ui.minWaterTemp, QOverload<double>::of(&QDoubleSpinBox::valueChanged),
 		this, &FilterWidget2::updateFilter);
 
 	connect(ui.fromDate, &QDateTimeEdit::dateChanged,
@@ -84,25 +79,25 @@ FilterWidget2::FilterWidget2(QWidget* parent) :
 	connect(ui.tags, &QLineEdit::textChanged,
 		this, &FilterWidget2::updateFilter);
 
-	connect(ui.tagsMode, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
+	connect(ui.tagsMode, QOverload<int>::of(&QComboBox::currentIndexChanged),
 		this, &FilterWidget2::updateFilter);
 
 	connect(ui.people, &QLineEdit::textChanged,
 		this, &FilterWidget2::updateFilter);
 
-	connect(ui.peopleMode, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
+	connect(ui.peopleMode, QOverload<int>::of(&QComboBox::currentIndexChanged),
 		this, &FilterWidget2::updateFilter);
 
 	connect(ui.location, &QLineEdit::textChanged,
 		this, &FilterWidget2::updateFilter);
 
-	connect(ui.locationMode, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
+	connect(ui.locationMode, QOverload<int>::of(&QComboBox::currentIndexChanged),
 		this, &FilterWidget2::updateFilter);
 
 	connect(ui.suit, &QLineEdit::textChanged,
 		this, &FilterWidget2::updateFilter);
 
-	connect(ui.suitMode, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged),
+	connect(ui.suitMode, QOverload<int>::of(&QComboBox::currentIndexChanged),
 		this, &FilterWidget2::updateFilter);
 
 	connect(ui.dnotes, &QLineEdit::textChanged,